diff --git a/Cargo.lock b/Cargo.lock
index 47c8d2ff5f4f..8c24727e932d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2101,6 +2101,7 @@ dependencies = [
  "libc 0.2.39 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "malloc_size_of 0.0.1",
+ "num-traits 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "regex 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "selectors 0.19.0",
  "size_of_test 0.0.1",
diff --git a/servo/ports/geckolib/tests/Cargo.toml b/servo/ports/geckolib/tests/Cargo.toml
index 078c6a3c66ab..746659b686bc 100644
--- a/servo/ports/geckolib/tests/Cargo.toml
+++ b/servo/ports/geckolib/tests/Cargo.toml
@@ -20,6 +20,7 @@ geckoservo = {path = "../../../ports/geckolib"}
 libc = "0.2"
 log = {version = "0.4", features = ["release_max_level_info"]}
 malloc_size_of = {path = "../../../components/malloc_size_of"}
+num-traits = "0.2"
 selectors = {path = "../../../components/selectors"}
 size_of_test = {path = "../../../components/size_of_test"}
 smallvec = "0.6"
diff --git a/servo/ports/geckolib/tests/lib.rs b/servo/ports/geckolib/tests/lib.rs
index 9981611d17a4..853f3cef9f7f 100644
--- a/servo/ports/geckolib/tests/lib.rs
+++ b/servo/ports/geckolib/tests/lib.rs
@@ -17,6 +17,7 @@ extern crate cssparser;
 extern crate geckoservo;
 #[macro_use] extern crate log;
 extern crate malloc_size_of;
+extern crate num_traits;
 extern crate selectors;
 extern crate smallvec;
 #[macro_use] extern crate size_of_test;